This invention relates to abrasive compacts.
Abrasive compacts are used extensively in cutting, milling, grinding, drilling and other abrasive operations. Abrasive compacts consist of a mass of diamond or cubic boron nitride particles bonded into a coherent, polycrystalline hard conglomerate. The abrasive particle content of abrasive compacts is high and there is an extensive amount of direct particle-to-particle bonding. Abrasive compacts are generally made under elevated temperature and pressure conditions at which the abrasive particle, be it diamond or cubic boron nitride, is crystallographically stable.
Abrasive compacts tend to be brittle and in use they are frequently supported by being bonded to a cemented carbide substrate or support. Such supported abrasive compacts are known in the art as composite abrasive compacts. The composite abrasive compact may be used as such in the working surface of an abrasive tool.
Examples of composite abrasive compacts can be found described in U.S. Pat. Nos. 3,745,623, 3,767,371 and 3,743,489.
Composite abrasive compacts are generally produced by placing the components, in powdered form, necessary to form an abrasive compact on a cemented carbide substrate. This unbonded assembly is placed in a reaction capsule which is then placed in the reaction zone of a conventional high pressure/high temperture apparatus. The contents of the reaction capsule are subjected to suitable conditions of elevated temperature and pressure.
Diamond abrasive compacts of the type described in the above mentioned U.S. patent specifications tend to be thermally sensitive and degrade when exposed to temperatures in excess of 700.degree. C. Diamond abrasive compacts are known which are thermally stable at temperatures well in excess of 700.degree. C. and these compacts are known as thermally stable diamond compacts. Examples of such compacts are described in British Patent No. 2158086 and U.S. Pats. Nos. 4,224,380 and 4,534,773.
As mentioned above, abrasive compacts are used in a variety of applications such as cutting, drilling, grinding and in mining picks. In some of these applications large abrasive compacts are used and this gives rise to spalling problems. Spalling occurs when cracks develop in or behing the cutting edge or point due to the large forces which act on that point or edge and the cracks propogate through the compact layer.
U.S. Pat. No. 4,525,179 describes a method of making a diamond or cubic boron nitride compact by providing partitions within the particulate mass which is placed in the high pressure/high temperature apparatus. The material of the strips is typically a metal of Group IIIB, IVB, VB, VIB, VIIB or VII or an alloy thereof. After sintering the partition layers are removed by leaching which will also remove the metallic phase present in the compact. What is produced is a plurality of smaller compacts of various shapes.
This specification also states that the embedded partition strips may remain in the sintered mass and serve as chip arresters which limit the movement of fractures within the diamond or cubic boron nitride compact. However, such compacts, depending on the nature of the material of the partition strip, are likely to be particularly temperature sensitive.